Schema Validation

Schema validation lets you create validation rules for your fields, such as allowed data types and value ranges.

MongoDB uses a flexible schema model, which means that documents in a collection do not need to have the same fields or data types by default. Once you've established an application schema, you can use schema validation to ensure there are no unintended schema changes or improper data types.

When to Use Schema Validation

Your schema validation needs depend on how users use your application. When your application is in the early stages of development, schema validation may impose unhelpful restrictions because you don't know how you want to organize your data. Specifically, the fields in your collections may change over time.

Schema validation is most useful for an established application where you have a good sense of how to organize your data. You can use schema validation in the following scenarios:

• For a users collection, ensure that the password field is only stored as a string. This validation prevents users from saving their password as an unexpected data type, like an image.
• For a sales collection, ensure that the item field belongs to a list of items that your store sells. This validation prevents a user from accidentally misspelling an item name when entering sales data.
• For a students collection, ensure that the gpa field is always a positive number. This validation prevents errors during data entry.

When MongoDB Checks Validation

After you add schema validation rules to a collection:

• All document inserts must match the rules.
• The schema validation level defines how the rules are applied to existing documents and document updates. To learn more, see Specify Validation Level for Existing Documents .

To find documents in a collection that don't match the schema validation rules, see Find Documents that Don't Match the Schema .

What Happens When a Document Fails Validation

By default, when an insert or update operation would result in an invalid document, MongoDB rejects the operation and does not write the document to the collection.

Alternatively, you can configure MongoDB to allow invalid documents and log warnings when schema violations occur.

Get Started

For common tasks involving schema validation, see the following pages:

• Specify JSON Schema Validation
• Specify Validation With Query Operators
• Specify Allowed Field Values
• View Existing Validation Rules
• Modify Schema Validation
• Query for and Modify Valid or Invalid Documents
• Bypass Schema Validation

Learn More

To learn about MongoDB's flexible schema model, see Data Modeling .